(1) Field of the Invention
The invention relates to means for preventing a propeller on a device subject to free-fall from rotating in a reverse direction during such free-fall, and more specifically to a propeller assembly in an underwater device having stop means for preventing reverse rotation of the propeller during sinking of the device in water.
(2) Description of the Prior Art
Underwater devices, such as acoustic countermeasure devices, are known which utilize a drive motor and propeller system for transiting and/or hovering in a water environment. During an ascent or in hovering, the propeller provides the thrust required to cause the device to rise, or refrain from sinking. During descent, however, the drive motor is off and the device sinks until buoyant forces on the device are balanced. It is during descent that the propeller typically is driven in the reverse direction by forces generated as the water flows over the propeller. Such reverse rotation of the propeller causes the electric drive motor to act as a generator, creating a back electromotive force, which can be problematic when the motor subsequently is energized. High current spikes can develop, causing burn-out of electronics. Further, delays can occur in the motor speed coming up to the desired level. Such problems have been addressed by the provision of additional electronics, which add to the cost and complexity of the device. Thus, there is a need for a relatively simple and inexpensive mechanical solution to the reverse rotation problem in acoustic countermeasure devices, and the like.